There are many applications where it is desired to know if and when two objects travelling in a medium have touched or not. For instance, turbine blades spinning at high speed in a nacelle will deteriorate and possible cause fatal destruction of the engine if they come in contact with the nacelle. In the game of cricket, the bat and ball are in an air medium and contact between the two objects determines fate of a batsmen. Similarly, in the game of tennis, when the ball touches the net during a serve, the serve has to be re-taken depending on where the ball lands. Other sports in which decisions are made based on objects touching the net are badminton, table tennis and other bat sports involving a net.
To date there have been numerous methods developed to determine contact between objects. For instance, Published U.S. Patent Application No. US20090017919A1, incorporated herein by reference as useful background information, describes an infra-red based approach where friction caused by contact of objects will alter the heat signature of both objected, the friction being capable of detection by a sufficient resolution thermal camera. This method has the disadvantage of the contacted objects being required to enter and remain in the observable plane of the camera for a sufficiently long time for the image to be resolved. Furthermore, the quality of the image is dependent on the amount of friction between the two objects as well as the infrared emitting wavelength of the material. Therefore this method requires a number of very expensive cameras in order to be effective.
Published PCT Application WO2000010333A1, incorporated herein by reference as useful background information, describes a technique that utilizes sound to determine the contact between two objects. This is a widely used technique since it requires only one reasonably high quality microphone to detect the sound. However, in order to disseminate the origin of the sound, medium-speed cameras are needed to resolve the conundrum. Also, as has been showed recently, there exists a condition where this method can create a false positive.
Vibration detection mechanisms have been suggested but have not been implemented on a wide range of equipment. This method relies on sensors that detect acoustic vibrations in equipment to inform on contact between objects. This method requires alterations of the equipment being used. Often these alterations are intrusive to the equipment, require mobile power sources, and require additional signal conditioning electronics. This method is also highly susceptible to false positives when objects are close to, but not touching each other.
False positives are a phenomenon where pressure waves generated in the medium by an object travelling though the medium, interact with a second object, causing vibrations in both the object and the medium. These vibrations will be measured by the acoustic and vibration sensors in the medium and objects respectively and be reported as contact between the bodies.